Apparatus for testing shock-absorbing struts for airplanes



Dec. 10, 1935 R, SHANLEY $1311 APPARATUS FOR TESTING SHOCK ABSORBING STRUTS FOR AIRPLANES F1166. May 5, 1933 5 Sheets-Sheet l I INVENTOR Dec. 10, 1935. F. R. SHANLEY APPARATUS FOR TESTING SHOCK ABSORBING STRUTS FOR AIRPLANES Filed May 5, 1953 I 5 Sheets-Sheet 2 ZM/F INVENTOR Patented Dec. 10, 1935 I UNITED STATES PA ENTfoFFIcEI f APPARATUS FOR TESTING SHOCK-ABSORB- ING STRUTS FOR AIRPLANES r Francis R. Shanley, Washington, D. C. Application May 3, 1933, Serial No. 669,242 11 Claims. (01. 265-13) This invention relates to improvements in apcombination as it is installed on the airplane. paratus for testing shock-absorbing units for As this is often impracticable and expensive. airplanes and provides a means whereby the conit is common practice to test the particular comditions actually existing on the airplane can be bination of shock-absorbing units in a special accurately reproduced in the test. testing machine. In certain cases this intro- 5 In the accompanying drawings: duces appreciable errors in the results. This can Figure 1 is a front view of an airplane showreadily be understood by referring to Figure 1, ing a typical .method of installing the shock where each shock-absorbing strut l is so installed absorbing struts. on the airplane that, for a given vertical load on Figure 2 is a schematic drawing illustrating the wheel and tire 2, a considerably greater load 10 the principle of the dynamic testing apparatus exists in the strut l. Likewise, for a given downin common use. ward displacement of the airplane body 3 with Figures 3, 4, 5, and 6 are schematic drawings respect to the ground, the distance through which illustrating various forms of the improved apthe strut I is compressed will not be the same as I paratus. the vertical movement of the axle 4 with respect 1:;

Figure '7 is a'geometrical constructionshowing to the airplane. The relative magnitude of the the action of the leverage system illustrated in forces, displacements, and velocities of the axle Figure 5. and shock-absorbing strut can readily be deter- Figures 8 and 9 are, respectively, front and mined for any airplane by ordinary geometrical side elevations of a typical installation embodymethods. i0 ing this invention. In the apparatus previously used for the test- In order that an airplane structure shall not ing of shock-absorbing struts the strut is tested be subjected to excessive loads on landing, it is in a vertical position and in line with the wheel necessary to incorporate a shock-absorbing and tire, as shown in Figure 2. In this figure 2 mechanism in the landing gear. It is often the shcck-absorbingstrut is represented by 5,

necessary to determine whether a certain shockthe wheel and tire by ii, and the weight box used absorbing mechanism will absorb the kinetic enin applying the load, by 1. The guides and other. ergy of the airplane without subjecting the airnecessary features are not shown. The appaplane structure to loads greater than those for ratus is used by allowing the system shown to which it has been designed. Although it is thedrop freely through a givemverticai distance, h, 80 oretically possible to analyze, mathematically, and obtaining, by means of suitableinstruments, the operation of a typical landing gear shockthe data required to determine the maximum absorbing mechanism, the mathematics involved load developed in the shock-absorbing strut 5, are usually very complicated and tedious. This It is obvious that the totalenergy'to be absorbed t is particularly true when a shock-absorbing strut at the instant of impact of the tire Bwith the 85 of the oleo type is used in conjunction with a base 8 is directly proportional to the mass of pneumatic tire, this combination being the most the freely-dropping apparatus and the initial commonly used on modern airplanes. It will be height of drop. appreciated that the pneumatic tire is, in itself, In cases where the shock-absorbing struts are 40 a shock-absorbing unit, as evidenced by the fact installed as shown in Figure 1, it is impossible to. 40 that on small airplanes the entire shock-absorbreproduce the conditions exactly by means of mg. capacity is often supplied by a pneumatic the apparatus illustrated in Figure 2. 'The load tire of suitable size.- Although the prediction on the tire 6 will be the same as the load on; of the shock-absorption capacity and characterthe strut 5, while the velocity of the strut pisistics of a pneumatic tire acting alone is relaton will not be correct if the correctheight of 45 tively simple, an entirely different situation exfree drop is used. Various means of correcting ists when apneumatic tire is used in conjunction the results have been tried, but none are comwith a shock-absorbing strut. In short, it is not pletely satisfactory. The situation is most seripossible to combine, in a simple manner, the reous in the case of hydraulic shock-absorbing sults of separate tests of a shock-absorbing strut struts, in which the velocity of the piston has a and a pneumatic tire. For this reason, the bemarked effect on the shock-absorption charachavior of a certain combination of shock-abteri'stics and therefore should always be the sorbing units consisting of ashock-absorbing same as it would .be in the actual installation. strut and a pneumatic tire can at present be The object of this invention is to eliminate determined accurately only by testing the entire the difiiculties enumerated above in a simple and 55 practical manner, thus enabling the true shockabsorption characteristics to be obtained without the necessity for a dynamic test of the complete landing gear structure and without recourse to compromising adjustments of the test values obtained from a straight drop-test.

The simplest form of this invention is shownin Figure 3. By comparison of Figure 3 with Figure 2 it will be seen that the shock-absorbing strut 9 will have a load approximately twice'as great as the load applied to the tire ill. The ratio of the load in the strut 9- to the load on the tire H) can be easily increased or decreased by moving the strut 9 closer to or farther away from I the member ll. Holes are provided in members l2, l2 for this purpose. If the correct load ratio is obtained by proper adjustment, it follows that the proper velocity ratio will also be obtained. The actual conditions existing on the. airplane therefore can be veryclosely reproduced. I

The apparatus diagrammatically illustrated in Figure 3 is not symmetrical and would require some form of counterbalancing such as indicated by the weight I 3. To eliminate the necessity for counterbalancing, the systems shown in Figures 4 or 5 may be used. In Figure 4 the shockabsorbing strut I 4 is symmetrically located and is connected with beams l5 l5 by the members l6, 16. This arrangement is almost equivalent to'a double arrangement of the leverage system shown in Figure 3, except that the loads from the levers l5, l5 are combined into a single load at each end of the strut H by' means of members i6, Hi. All the joints shown are pin joints. ,7

In Figure 5, the arrangement at the top of the strut I1 is identical with that of Figure 4, but the members l8, I8 are attached directly to the wheel fork l9, thereby eliminating several'memw bers.

Figure 6 illustrates how this apparatus would be used for testing shock absorbing' struts in which the strut load is less than the wheel load. Inthis case the members 20, 20 would be in com pression during the test. .Members 2|, 2| are independent of each other except that they are joined to the weight box by a common point, 24. It is obvious that the load in the shock-absorbing strut 22'is decreased below the wheel load when members 20, 20 are attached to meme bers 2|, 2| on opposite sides of the centeripivot 24 from members 23, 23, as shown Figure 7 is a centerlinedrawing oi. an arrangement such as shown in Figure 5. The'members bc are shown attached to members wd so that the load in the strut'b-e will equal twice the load applied at a. The dotted lines indicate the deflected position of the system. By inspection it will be seen that the distance b-b' is very nearly one-half the distance H, which is the desired relationship. The slight error introduced in using the particular arrangement illustrated in Figure 5 is not serious enough to war-' rant using a more elaborate leverage system. It is therefore believed that the arrangements illustrated in Figures 5 and 6 will suffice for the testing of all shock-absorbing struts which are installed on the airplane in such a manner ,that the ratio between the load in the shock strut and the load on the wheel axle is diiferent from unity.

Figures 8 and Q represent views of a typical dynamic-testing apparatus in which the principles of this invention have been incorporated. Only the major parts are shown, the usual instruments for measuring load, deflection, acceleration, and

so forth, having been omitted. The use of at least one of such instruments is, of course, essential to the procuring of records during a test, but since such usage is well understood by those acquainted with the art, no attempt has been 5 made to illustrate the various instruments in the drawings.

In Figures 8 and 9 the wheel and tire 25 are attached to the fork 26 by means of the axle 21. The fork 25 is restrained to travel vertically along the upright members 28, 28 by means of the guides 29, 2B. The shock-absorbing strut 30 is attached to the fork 26 at one end and to levers 3|, 3! at the other end. Levers 3|, 3| are attached to beams 32, 32 in such a way that their point of attachmentcan be changed to give the desired ratio between the load in the shockabsorbing strut 30 and the load applied at joint 33 by the weight box 34. The outer ends of members 32, 32 are connected to the fork 26 by means of members 35, 35. Weights 36 are placed in the weight box 34 to give the required total test load. Weight box 34 is provided with guides 31, 31 to restrain it to travelv along the vertical members 28, 20. A quick-release mechanism 38 is used to hold the assembly at the desired height and to permit the weight box 34 to be released by the operator. The height of free drop above the base 39 can be adjusted by varying the position of cr'ossmember 40. Means for raising the assembly after dropping are indicated by the hoist cable H. p c

It will be appreciated that this invention will be used largely for testing the particular combination of shock-absorbing units represented by a shock-absorbing strut and a pneumatic tire. This combination has accordingly been illustrated in the drawings. The apparatus can, of course, be used for other combinations of shockabsorbing units or for a single shock-absorbing 40 I unit. The latter case would be exemplified by a landing gear installation such as shown in Figure 1 employing a hard tire having no shockabsorbing properties.

Summarizing: the apparatus illustrated in Figures 8 and 91s used for the dynamic-testing Ofshock-absorbing units in the same manner as the conventional apparatus, the essential difference being that the correct ratio between the basic load in the shock-absorbing strut and the basic load onv the tire can be obtained by varying the upper point ,of attachment of levers 3|,

3| to beams 32, 32, whereas in the conventional system such an adjustment is impossible. This improvement permits the correct height of drop, as well as the correct basic tire load, ,to be used in the test. The relative velocity of the moving parts of the shock-absorbing strut will also be correct. Instruments for measuring the load in the shock-absorbing strut, the velocity of the various components, and any other desirable quantities may be used in conjunction with this apparatus without changing the mode of operation and without the addition of any novel features to the invention herein described.

I claim:

' 1. An apparatus for dynamically testing shockabsorbing units used in airplane landing gear, by means of which the forces which would act on a shock-absorbing unit in a dynamic test of an airplane landing gear are closely reproduced, consisting of means for supplying kinetic energy through the use of a moving mass and means for causing said kinetic energy to be absorbed by the shock-absorbing unit, the second-mentioned 75 means including a leverage system which transmits a decelerating force to said moving mass and at the same time applies to said shock-absorbing unit a force difierent in magnitude from said decelerating force, the ratio between said forces being determined by the arrangement of said leverage system so as to approximate closely the ratio which would exist in the actual airplane.

2. An apparatus for testing combinations of shock-absorbing units used in airplane landing gear, by means of which the forces which would act on the shock-absorbing units in a dynamic 7 test of an airplane landing gear are closely reproduced, consisting of means for supplying kinetic energy through the use of a moving mass and means for causing said kinetic energy to be absorbed by a combination of shock-absorbing units, the second-mentioned means including a leverage system which transmits a decelerating force to said moving mass and at the same time applies forces to each of said shock-absorbing units, each of the last mentioned forces being of different magnitude and proportioned by the arrangement of said leverage system so as to approximate closely the proportion which would exist in the actual airplane.

3. An apparatus as described in claim 1, in which additional means are provided for adjusting the ratio of the decelerating force to the force on the shock-absorbing unit to any desired value.

4. An apparatus as described in claim 2, in which additional means are provided for adjusting the ratio between the forces acting on the shock-absorbing units to any desired value.

5. An apparatus as described in claim 1, in which the leverage system is substantially symmetrical with respect to the centerline of the shock-absorbing unit,

6. An apparatus as described in claim 2, in which the shock-absorbing units are in line with and the leverage system is symmetrically disposed about the centerline of travel of the mass.

'7. An apparatus as described in claim 1, in

which means are included for balancing the inertia forces of the apparatus about the centerline of travel of the mass. v

8. In an apparatus for dynamically testing shock-absorbing units, a leverage system adapted to be symmetrically disposed about a shock-absorbing unit, the members of said leverage system being pivotally connected in such a manner that a given deflection of the leverage system in the direction of motion of said shock-absorbing unit will produce a deflection of different magnitude in the shock-absorbing unit, the ratio between said deflections being determined by the arrangement of said leverage system so as to approximate closely the ratio which would exist in the actual airplane.

9. In an apparatus for dynamically testing shock-absorbing units, a leverage system as described in claim 8, in which means are included for varying the geometrical relationship of the n pivotally connected members in such a way that the ratio of the deflection of the leverage system to the deflection of the shock-absorbing unit can be adjusted to any desired value.

10. A leverage system for loading a shock-absorbing strut, comprising a member through which a force is applied to the system, two beams pivotally connected to said member, a second member attached to one end of the shock-absorbing strut, two arms pivotally attached to opposite ends of said beams and pivotally connected to said second member, two more arms pivotally attached at a common point on the other end of said shock-absorbing strut, the other ends of the last-mentioned arms being pivotally attached at points on said beams equidistant from the point of attachment of said beams to the first-mentioned member, the entire leverage system being symmetrically disposed about the centerline of said shock-absorbing unit.

11. A leverage system as described in claim 10, in which means are provided for varying the points of attachment of the last-mentioned arms to the beams.

FRANCIS R. SHANLEY. 

